Availability of Coal Resources for Mining in Illinois

Transcription

1 OFS Availability of Coal Resources for Mining in Illinois Albion South, Peoria West, Snyder-West Union, Springerton, and Tallula Quadrangles, Clark, Edwards, Hamilton, Menard, Peoria, Sangamon, and White Counties Colin G. Treworgy, Jamie L. McBeth, Cheri A. Chenoweth, Christopher P. Korose, and Daniel L. North Open File Series Department of Natural Resources ILLINOIS STATE GEOLOGICAL SURVEY William W. Shilts, Chief Natural Resources Building 615 East Peabody Drive Champaign, Illinois (217)

2

3 CONTENTS ACKNOWLEDGEMENTS iv EXECUTIVE SUMMARY 1 INTRODUCTION 2 Selection of Quadrangles 2 Coal Resource Classification System 2 Sources of Data 4 Previous Investigations 4 FACTORS AFFECTING THE AVAILABILITY OF COAL 4 Surface Minable Coal 6 Depth of Seam 6 Thickness of Seam 6 Stripping Ratio 6 Thickness of Bedrock and Unconsolidated Overburden 6 Size and Configuration of Mining Block 7 Land Use 7 Abandoned Mine Workings 8 Underground Minable Coal 8 Depth of Seam 8 Thickness of Seam 8 Thickness of Bedrock and Unconsolidated Overburden 8 Thickness of Interburden Between Seams 9 Faults 9 Partings 9 Dykersburg Shale 11 Anvil Rock Sandstone 11 Galatia Channel 12 Size and Configuration of Mining Block 13 Land Use 13 Abandoned Mine Workings 15 Coal Available, but With Conditions 15 Closely-Spaced Wells 15 Potential Land Use Conflicts 16 Coal Quality Limitations 16 AVAILABLE RESOURCES 17 Availability of Coal in the Peoria West Quadrangle, Western Illinois 17 Geology and Coal Resources 17 Available Coal 22 Availability of Coal in the Tallula Quadrangle, West-Central Illinois 33 Geology and Coal Resources 33 Available Coal 45 Availability of Coal in the Albion South and Springerton Quadrangles, Southern Illinois 50 Geology and Coal Resources 50 Available Coal 67 Availability of Coal in the Snyder-West Union Quadrangle, East-Central Illinois 74 Geology and Coal Resources 74 Available Coal 84 CONCLUSIONS 85 REFERENCES 90 i

4 TABLES 1 Summary of the original resources and their availability for mining in the Albion South, Peoria West, Snyder-West Union, Springerton, and Tallula Quadrangles 1 2 Criteria used to define available coal in the Albion South, Peoria West, Snyder-West Union, Springerton, and Tallula Quadrangles 5 3 Minimum thickness of bedrock and maximum thickness of unconsolidated deposits surface minable for specified thicknesses of overburden 8 4 Availability of coal resources for mining in the Peoria West Quadrangle 25 5 Availability of coal resources for mining in the Tallula Quadrangle 46 6 Availability of coal resources for mining in the Albion South Quadrangle 67 7 Availability of coal resources for mining in the Springerton Quadrangle 68 8 Availability of coal resources for mining in the Snyder-West Union Quadrangle 84 FIGURES 1 Coal resource regions and quadrangle study areas 3 2 Problems encountered in surface and underground mines that have overburden consisting of thick unconsolidated sediments over thin bedrock 7 3 Unmined areas adjacent to one of the faults in the Wabash Valley Fault System 10 4 Examples of partings in the Springfield Coal in the Springerton Quadrangle 11 5 Extent of the Dykersburg Shale and the Galatia Channel and the location of quadrangles studied 12 6 Areas of adverse mining conditions in the Springfield Coal near the Galatia Channel 13 7 Areas of Herrin Coal eroded by Anvil Rock channels 14 8 Unfavorable mining conditions associated with the Anvil Rock Sandstone and Wabash Valley Fault System in southeastern Illinois 15 9 Selected stratigraphic units, Peoria West Quadrangle Surface features, Peoria West Quadrangle Thickness of the Danville Coal, Peoria West Quadrangle Thickness of the Herrin Coal, Peoria West Quadrangle Depth of the Herrin Coal, Peoria West Quadrangle Thickness of the Springfield Coal, Peoria West Quadrangle Depth of the Springfield Coal, Peoria West Quadrangle Availability of coal resources, Peoria West Quadrangle Availability of the Danville Coal for surface mining, Peoria West Quadrangle Availability of the Herrin Coal for surface mining, Peoria West Quadrangle Availability of the Herrin Coal for underground mining, Peoria West Quadrangle Availability of the Springfield Coal for surface mining, Peoria West Quadrangle Availability of the Springfield Coal for underground mining, Peoria West Quadrangle Availability of the Colchester Coal for mining, Peoria West Quadrangle Selected stratigraphic units, Tallula Quadrangle Surface features, Tallula Quadrangle Elevation of the bedrock surface, Tallula Quadrangle Thickness of the Herrin Coal, Tallula Quadrangle Depth of the Herrin Coal, Tallula Quadrangle Stripping ratio of the Herrin Coal, Tallula Quadrangle Thickness of the Springfield Coal, Tallula Quadrangle Depth of the Springfield Coal, Tallula Quadrangle Stripping ratio of the Herrin and Springfield Coal combined, Tallula Quadrangle Thickness of unconsolidated overburden, Springfield Coal, Tallula Quadrangle Thickness of bedrock overburden, Springfield Coal, Tallula Quadrangle Ratio of bedrock to unconsolidated overburden, Springfield Coal, Tallula Quadrangle Availability of coal resources, Tallula Quadrangle Availabilty of the Herrin Coal for surface mining, Tallula Quadrangle Availability of the Springfield Coal for surface mining, Tallula Quadrangle Availability of the Springfield Coal for underground mining, Tallula Quadrangle 49 ii

5 39 Selected stratigraphic units, Albion South and Springerton Quadrangles Surface features, Albion South Quadrangle Surface features, Springerton Quadrangle Well locations, Albion South Quadrangle Well locations, Springerton Quadrangle Elevation of the Herrin Coal, Albion South Quadrangle Thickness of the Herrin Coal, Albion South Quadrangle Thickness of the Herrin Coal, Springerton Quadrangle Thickness of the Springfield Coal, Albion South Quadrangle Thickness of the Springfield Coal, Springerton Quadrangle Thickness of the Dykersburg Shale, Albion South Quadrangle Thickness of the Dykersburg Shale, Springerton Quadrangle Thickness of the Lower Dekoven Coal, Springerton Quadrangle Thickness of the Davis Coal, Springerton Quadrangle Thickness of the interval between the Lower Dekoven and Davis Coals, Springerton Quadrangle Yield of clean coal per ton of material mined, Lower Dekoven and Davis Coals, Springerton Quadrangle Availability of coal resources, Albion South Quadrangle Availability of coal resources, Springerton Quadrangle Availability of the Herrin Coal for underground mining, Albion South Quadrangle Availability of the Herrin Coal for underground mining, Springerton Quadrangle Availability of the Springfield Coal for underground mining, Albion South Quadrangle Availability of the Springfield Coal for underground mining, Springerton Quadrangle Availability of the Davis and Lower Dekoven Coals for underground mining, Springerton Quadrangle Selected stratigraphic units, Snyder-West Union Quadrangle Surface features, Snyder-West Union Quadrangle Depth of the Danville Coal, Snyder-West Union Quadrangle Thickness of the Danville Coal, Snyder-West Union Quadrangle Extent of the Jamestown Coal, east-central Illinois Thickness of the Jamestown Coal, Snyder-West Union Quadrangle Thickness of the interval between the Danville and Jamestown Coals, Snyder-West Union Quadrangle Thickness of the Springfield Coal, Snyder-West Union Quadrangle Thickness of the Seelyville Coal, Snyder-West Union Quadrangle Yield of clean coal per ton of material mined, Seelyville Coal, Snyder-West Union Quadrangle Availability of coal resources, Snyder-West Union Quadrangle Availability of the Danville Coal for underground mining, Snyder-West Union Quadrangle Availability of the Jamestown Coal for underground mining, Snyder-West Union Quadrangle Availability of the Springfield Coal for underground mining, Snyder-West Union Quadrangle Availability of the Seelyville Coal for underground mining, Snyder-West Union Quadrangle 89 iii

6 ACKNOWLEDGMENTS We are especially appreciative of the information on criteria that limit the availability of coal given to us by mining experts. This report draws on information obtained from experts interviewed for previous reports in this series as well as interviews for this report conducted with Brent Dodrill and Edwin Settle, Consolidation Coal Company; Philip Ames and Bruce Dausman, Black Beauty Coal Company; and Alan Kern, Jim Brown, and Michael Meighan, White County Coal Company. Additional information was obtained from John Popp, Mapco Inc.; Marvin Thompson, consulting geologist; and John Williams, Amax Coal Company. This project was supported by the U.S. Geological Survey, Department of the Interior, under assistance award No HQ-97-AG The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. This manuscript is published with the understanding that the U.S. Government is authorized to reproduce and distribute reprints for governmental use. The Illinois State Geological Survey considers its publications to be in the public domain. iv

7 EXECUTIVE SUMMARY This report is one of a series examining the availability of coal resources for mining in Illinois. It describes mapping of coal resources and related geologic features in five quadrangles (Albion South, Peoria West, Snyder-West Union, Springerton, and Tallula). Coal company and state government experts were interviewed to determine how regulatory restrictions, cultural features, mining technology, and geologic, economic, and environmental conditions affect resource availability in the five quadrangles. Mining conditions in the Peoria West and Tallula Quadrangles are representative of those associated with surface and shallow underground mining of the Herrin and Springfield Coals in the west-central portion of Illinois. The Peoria West Quadrangle is located in a near urban setting and the Tallula Quadrangle is located in a rural setting. Conditions in these quadrangles demonstrate how suburban development and the thickness of unconsolidated overburden relative to bedrock overburden restrict the availability of surface and underground minable resources. The Albion South and Springerton Quadrangles are representative of mining conditions in that part of the Illinois Basin in southeastern Illinois where the coal lies at considerable depth. Mining conditions associated with the peat-contemporaneous Galatia Channel, the post-peat Anvil Rock Channel, wide fault zones, and areas of closely-spaced oil wells are some of the conditions that restrict the availability of resources in this area. The Snyder-West Union Quadrangle is representative of mining conditions on the east-central margin of the basin. This is the only region in the state where the Jamestown Coal is thick enough to mine underground and one of only a few regions where the Danville and Seelyville Coals are underground minable. The thickness of interburden between the Danville and Jamestown Coals and partings in the Seelyville Coal were found to impose significant restrictions on available resources. The tonnage of the original coal resources and the percentage available for mining in each quadrangle are shown in table 1. The category Available with Conditions is used for resources that meet the criteria for available coal, but have some additional characteristic that may ultimately limit their availability. In the Albion South and Springerton Quadrangles these are resources in areas of closely-spaced oil wells. Coal can and has been mined in such areas, but mining costs are higher and the use of longwall equipment may be impractical. In the Tallula Quadrangle and in part of the Peoria West Quadrangle, the conditionally available resources are resources that will only be recovered if the underlying seam is surface mined. Most of the conditionally available resources on the Peoria West Quadrangle are in areas where there are potential conflicts between mining and patterns of community development. Although mining is not legally restricted in these areas, the high land values, ongoing suburban development, potential for community opposition to or interference with mining activities, and long term liability for surface subsidence make it unlikely that mining will be attempted. In the Snyder-West Union Quadrangle, most resources are believed to have chlorine contents of close to 0.5% or higher. Although coal with this chlorine content can be used, there is no current market for the coal, and no coal in Illinois with this high of a chlorine content is being mined. Technological factors such as stripping ratio, thickness of unconsolidated and bedrock overburden, thickness of interburden, block size, low yield of clean coal due to partings, and poor mining conditions associated with faults, channels, partings, and roof stratigraphy restrict the availability of 22% to 72% of the resources in each quadrangle. Land-use features (towns, roads, railroads, cemeteries, abandoned mines) restrict another 1% to 39% of the resources. Peoria West is the only one of the quadrangles studied that has had any significant mining. About 11% of the original resources have been mined out. Table 1 Summary of the original resources and their availability for mining in the Albion South, Peoria West, Snyder-West Union, Springerton, and Tallula Quadrangles; millions of tons and (percent of original resources). Quadrangle Original Mined out Available W/conditions Technological Land use Albion South (0) 363 (50) 39 (5) 311 (43) 13 (2) Peoria West (11) 10 (2) 115 (23) 117 (25) 188(39) Snyder- West Union 1,027 0 (0) 0 (0) 432 (42) 587 (57) 8 (1) Springerton (0) 602 (67) 77 (9) 205 (23) 16 (2) Tallula (1) 40 (11) 12 (3) 258 (72) 43(12) 1

8 INTRODUCTION Accurate estimates of the amount of coal resources available for mining are needed for planning by federal and state agencies, local communities, utilities, mining companies, companies supplying goods and services to the mining industry, and other energy consumers and producers. Current inventories of coal resources in Illinois provide relatively accurate estimates of the total amount of coal in the ground (e.g. Treworgy et al. 1997b), but the actual percentage that is minable is not well defined. Environmental and regulatory restrictions, the presence of towns and other cultural features, current mining technology, geologic conditions, and other factors significantly reduce the amount of coal available for mining. Recognizing this difference between the reported tonnage and the tonnage of actual minable coal, the United States Geological Survey (USGS) initiated a program in the late 1980s to assess the amount of available coal in the United States (Eggleston et al. 1990). As part of this ongoing, cooperative effort, the Illinois State Geological Survey (ISGS) is assessing the availability of coal resources for future mining in Illinois. This report assesses the availability of coal resources in five quadrangles: Albion South, Peoria West, Snyder-West Union, Springerton, and Tallula (fig. 1). It also discusses the implications of these findings to the availability of coal for mining in larger regions of the state. The background of this program and a detailed description of the framework for the investigations in Illinois are provided in previous reports (e.g. Treworgy et al. 1994). Selection of Quadrangles Treworgy et al. (1994) divided Illinois into seven regions, each representing a distinct combination of geologic and physiographic characteristics (fig. 1), and selected two to four quadrangles representative of the mining conditions in each region. Quadrangle selection and resource assessment both focus on resources that have the highest potential for development (e.g. thick or lower sulfur content seams). This approach ensures that the most economically important deposits receive sufficient study and that little time is spent on coal that is unlikely to ever become available for mining. Maps at 1:24,000-scale showing the major coal seams, related geology, mines, and land use in each quadrangle were compiled based on previous regional investigations of mining conditions, resources, and geology. These maps provided the basis for detailed discussions with experts from mining companies, consulting firms, and government agencies active in the Illinois mining industry to identify the factors that affect the availability of coal in each quadrangle. Each quadrangle was discussed with three or more experts to develop a set of criteria defining available coal. These rules were then applied to each quadrangle to calculate the available resources and identify the factors that restrict significant quantities of resources from being minable. The quadrangles studied for this report were selected to provide data for several objectives. The Peoria West Quadrangle is the fourth quadrangle to be assessed in region 2 and completes the set of individual quadrangle studies of mining conditions in that region. There has been extensive mining in the quadrangle, but significant surface minable and shallow underground minable resources remain. The ongoing growth of nearby urban areas raises the potential for conflicts between mining and other land use. The Tallula Quadrangle represents mining conditions along the subcrop of the Herrin and Springfield Coals in region 3 and completes the set of studies planned for that region. The Albion South and Springerton Quadrangles complete the quadrangle studies planned to assess major deposits of low to medium sulfur Springfield Coal in southeastern Illinois (regions 4 and 7), as well as deep underground minable deposits of the Herrin and Davis Coals. The Snyder-West Union Quadrangle is the first study of this series that looks at the coal resources in east-central Illinois (region 5). This area contains significant resources in several seams that are only minable in limited areas of the state: the Danville, Jamestown, Survant, and Seelyville. Coal Resource Classification System The ISGS follows the terms and definitions of the USGS coal resource classification system (Wood et al. 1983). With minor modifications to suit local conditions, these definitions provide a standardized basis for compilations and comparisons of nationwide coal resources and reserves. 2

9 Figure 1 Coal resource regions and quadrangle study areas 3

10 The term original resources refers to the amount of coal resources originally in the ground prior to any mining. The ISGS has traditionally defined resources as all coal in the ground that is 18 or more inches in thickness and less than 150 feet deep, or all coal 28 or more inches thick. This definition was modified for this report to include coal less than 200 feet deep and at least 12 inches thick. These modifications were made to provide consistency with our estimates of original and available resources in the quadrangles previously studied. The term available coal is not a formal part of the USGS system, although it is commonly used by the USGS and many state geological surveys. Available coal, as used in this report, does not imply that particular coal deposits can be mined economically at the present time. Rather, the term designates deposits that have no significant characteristics likely to make them technically, legally, or economically unminable for the foreseeable future. Determining the actual cost and profitability of these deposits requires further engineering and marketing assessments. Sources of Data Geologic data for this study were compiled from drillers logs, core descriptions, and geophysical logs from coal and oil tests. Mine boundaries were compiled from the best available mine map for each mine. In cases where no map was available, the location of the mine was marked with a point symbol and, if possible, the general area of mining was delineated. Surface elevations were acquired from USGS 7.5-minute topographic maps. Information on land cover features such as cemeteries, roads, railroads, and towns were compiled from topographic maps or extracted from USGS Digital Line Graph files. All major surface features were verified by field reconnaissance. The coal resources in the Peoria West Quadrangle were mapped for previous studies (Cady 1952, Smith and Berggren 1963). No significant new stratigraphic data are available for this quadrangle, so the thickness and depth maps from the previous studies were used for this assessment of available coal. Previous Investigations The ISGS has evaluated the availability of coal resources in thirteen other quadrangles located in the northwestern, central, and southern parts of the state (Treworgy et al. 1994, Treworgy et al. 1995, Jacobson et al. 1996, Treworgy et al. 1996a, 1996b, and Treworgy et al. 1997a). Seventeen coal seams have been assessed in these studies. The coal found to be available for mining in each quadrangle ranged from as little as 18% to as much as 79% of the original resources. Each quadrangle represents a different geologic and geographic setting in Illinois and each quadrangle study identifies and defines factors that influence the availability of resources in that setting. Some factors, such as roof conditions, are different for each seam while other factors, such as minimum seam thickness, are applicable to all seams. Some factors, such as cemeteries, have the same effect on mining throughout the state while the effects of other factors, such as roads, are dependent on the region of the state and value of the underlying coal. FACTORS AFFECTING THE AVAILABILITY OF COAL Most factors that restrict mining are based on economic and social considerations and are not absolute restrictions on mining. Companies can choose to mine in areas of severe roof or floor conditions if they are willing to bear the higher operating costs, interruptions and delays in production, and lower employee morale that result from operating in these conditions. It is possible to surface mine through most roads and undermine small towns if a company is willing to invest the time and expense necessary to gain approval from the appropriate governing units and individual landowners, and to mitigate damages. Previous economic and social conditions have at times enabled companies to mine in areas where some factors are now restrictive. The current highly competitive price environment in the coal industry, which makes coal that is more expensive to mine uneconomic, is expected to prevail in the Illinois Basin indefinitely. Therefore, the criteria used to determine available coal for this report are likely to cover mining conditions for the foreseeable future. The following factors, which define available coal in the five quadrangles are a composite set of rules based on our interviews with mining companies (table 2). The restrictions are organized according to the mining method they apply to; surface or underground mining as currently practiced in Illinois. 4

11 Table 2 Criteria used to define available coal in the Albion South, Peoria West, Snyder-West Union, Springerton, and Tallula Quadrangles. Surface Mining Technological Restrictions Minimum seam thickness Main seam: 1 foot Overlying seams: 0.5 feet Underlying seams: 1 foot Maximum depth: 200 feet Maximum glacial and alluvial overburden: see table 3 Stripping ratio (cubic yards of overburden/ton of raw coal; volumes and weights not adjusted for swell factors or cleaning losses): Maximum: 25:1 Maximum average: 20:1 Minimum size of mine reserve (clean coal) Cumulative tonnage needed to support a mine and preparation plant: 10 million tons Individual block size: Less than 40 ft of overburden: 150 thousand tons More than 40 ft of overburden: 500 thousand tons Land use restrictions 100 ft buffer: Cemeteries, Railroads, State highways, Other paved roads (Peoria West only), High voltage transmission towers 200 ft buffer: Large underground mines 500 ft buffer: Subdivisions 2,640 ft buffer: Towns Underground Mining Technological Restrictions Minimum seam thickness: 3.5 ft Minimum bedrock cover: Springfield Coal on the Peoria West Quadrangle and all coals on the Tallula Quadrangle: 75 ft Herrin Coal on the Peoria West Quadrangle: 40 ft Minimum size of mining block (clean coal): Peoria West, Tallula: 20 million tons Albion South, Snyder-West Union, Springerton: 40 million tons Albion-Ridgeway Fault: no mining within 1,000 ft Galatia Channel: no mining of the Springfield Coal within 2,640 ft Dykersburg Shale: no mining in the Springfield Coal in areas with abrupt changes in shale thickness Anvil Rock Sandstone: no mining of the Herrin Coal where sandstone is less than 5 ft above the coal or within 1,800 ft of the main channel Partings: Minimum yield: 65% clean coal recovered per ton of material mined No mining of coal with partings greater than 1 ft thick over extensive areas (e.g. 40 acres or more) No mining individual benches of Springfield Coal where partings are more than 3 ft thick Land use restrictions 200 ft buffer: Abandoned mines 100 ft buffer (Peoria West), 200 ft (Snyder-West Union, Tallula), 400 ft (Albion South, Springerton): Towns and subdivisions, churches and schools, cemeteries, high voltage transmission towers (Peoria West), interstate highways, airports Available with Conditions Only if surface mined in combination with overlying or underlying seam: Resources meet criteria for stripping ratio and/or block size only when combined with resources in an underlying or overlying seam. Closely-spaced oil wells: Areas of 4 or more active or abandoned wells on 20 acre spacings or closer Potential land use conflicts: All otherwise available surface or underground minable coal within 2,640 ft of towns or subdivisions in areas where land use patterns are incompatible with mining. Coal quality limitations: resources with chlorine contents > 0.4% 5

12 Surface minable coals were found in the Peoria West and Tallula Quadrangles. All quadrangles contained underground minable coal. Surface Minable Coal Depth of Seam Depending on their thickness, coals less than 175 to 200 feet deep can be mined by either surface methods or underground methods (provided there is sufficient bedrock cover). The choice of surface or underground methods will depend on the comparative cost of extraction and the overall character of a company s reserves at a specific site. For example, if a company s reserve block is primarily deeper than 150 feet, it may elect to mine all of the coal by underground methods. Coals may be unavailable for surface mining due to their stripping ratio, a function of depth and thickness. Stripping ratio is discussed separately below. Thickness of Seam The minimum thickness of coal for surface mining is 1 foot for the lowermost seam in an interval to be mined, and 0.5 feet for overlying seams within the interval. Thinner seams are impractical to recover because the amount of out-of-seam dilution becomes too great a percentage of the material handled. Stripping Ratio The stripping ratio is the ratio of cubic yards of overburden that must be removed to recover one ton of coal. Whereas the thickness and depth of coal that can be economically mined are controlled in part by technical factors such as mining equipment, the maximum stripping ratio is strictly an economic limit. Coals with high stripping ratios may be more economical to mine by underground methods or may remain unmined until the market price for coal rises relative to production costs. Companies calculate stripping ratios on the basis of the anticipated tonnage of clean coal that will be produced. This calculation requires assumptions about the type and performance of mining and washing equipment to be used, as well as tests of the washability of the coal. For this study, the stripping ratios are based on the tonnage of in-place coal. This tonnage excludes partings, commonly clastic sediment deposited in the peat by nearby streams. This tonnage is probably 5 to 15 percent higher than the actual tonnage of clean coal after mining and cleaning losses. Some companies use a swell factor to account for the increase in volume of overburden after it is blasted. Swell factors for lithologies typically encountered in Illinois mines range from 1 (no swell) for sand to 1.7 for shale (Allsman and Yopes 1973). Although this is a large range, this swell factor requires such detailed site-specific knowledge about the quantities of different lithologies in the overburden (e.g. shale, limestone, sand, clay), that we could not use it in our calculations. Cubic yards of overburden were calculated simply from the total thickness of consolidated and unconsolidated material overlying the coal. For this study, the maximum stripping ratio adopted for available coal was 25 cubic yards of overburden per ton of in-place coal (25:1). The maximum average stripping ratio for any mining block was 20:1. Because we have not used clean coal tonnages or swell factors, these ratios are higher than the limits currently used by most companies. Thickness of Bedrock and Unconsolidated Overburden Thick deposits of glacial drift or alluvial sediment can restrict surface mining because of their potential to slump into the pit, fail under the weight of large draglines, and allow excessive groundwater flow into the pit (fig. 2). A minimum amount of bedrock overburden is needed to ensure that the coal is not weathered, and to provide stable material to hold the toe of the spoil pile. The maximum thickness of unconsolidated material that can be handled is dependent on the lithologic composition of the overburden, its physical properties (e.g. load bearing capacity, permeability), and the presence or absence of groundwater. The minimum bedrock and maximum glacial drift thicknesses that were handled by the companies we interviewed also depended on the mining plan and the type of equipment they were using to remove overburden. We did not compile sufficient information to assess the lithology and physical properties of the unconsolidated sediment in the quadrangles studied. The experience of the companies suggests that for an overburden thickness of 50 feet or less, a minimum of 10 feet of bedrock cover is needed. For overburden between 50 and 100 feet thick, one-third to one-half the material should be bedrock (table 3). The maximum thickness of unconsolidated overburden that can be handled over a large mining area is 6

13 approximately 50 feet. Small areas of thicker unconsolidated overburden can be mined, but large areas of thick unconsolidated overburden will be avoided. Size and Configuration of Mining Block A mine reserve must contain sufficient tonnage to allow companies to recover the costs of developing a mine (e.g. drilling, land acquisition, construction of surface facilities, initial box cuts and shafts, and purchase of equipment). Because of lower development costs, greater equipment mobility, and flexibility in operating plans, surface mines can be developed with smaller reserves and mining blocks than underground mines. Surface mines can be developed using trucks and earthmoving equipment that can be readily transported to the site. Although there are exceptions, most Illinois coals are cleaned to some degree before final shipment. The coal can be trucked from the mine pit over the existing road network to a central preparation plant. The minimum reserve for a surface mine is 10 million saleable tons. For this study we assumed that this is equivalent to about 12.5 million tons of raw coal in place. The reserve may be distributed among a number of adjacent blocks. Each mining block should contain at least 150 thousand tons of saleable coal if the coal is less than 40 feet deep or 500 thousand tons if the coal is greater than 40 feet deep. Land Use Although any land use or surface feature can be undermined or mined through if a company obtains permission from the owner and agrees to repair damages, companies generally find it impractical to mine under or through certain features because of the expense of restoring the feature, or the social and political hurdles required to obtain the necessary permission. This study considers all coal under towns, rural subdivisions, railroads, airports, high voltage transmission towers, schools, churches, and cemeteries as unavailable for surface mining. Roads can be a significant barrier to surface mining. Because of local opposition to mining and the relatively low value of coal beneath roads (because of seam thickness), most roads in the western and northwestern parts of the state, including the Peoria West Quadrangle, are considered a restriction to surface mining. In southern Illinois, the general acceptance of surface mining by the local population A. Slumping of mine highwall B. Water-bearing zones C. Roof falls D. Floor squeezes B glacial drift & alluvium bedrock Coal seam A C B x x x x x x x x x x x x x x x x x x x x mine x xx D x x x x x x x x x x x underclay Figure 2. Problems encountered in surface and underground mines that have overburden consisting of thick unconsolidated sediments over thin bedrock. 7

14 and the higher tonnage of coal per acre make it feasible for companies to surface mine through lightly used roads. We considered only state and federal highways to be a restriction to surface mining in the Tallula Quadrangle. A buffer of unmined coal must be left around any property or surface feature that cannot be disturbed. State law requires that surface mines leave a 100 foot buffer around churches and schools. Although the law requires only a 100 foot buffer around dwellings, in practice a larger buffer is left around towns because of the potential disturbance by dust, vibrations from blasting, and disruption of water wells. We used a buffer of 500 feet around rural subdivisions and a half mile around towns. Abandoned Mine Workings Illinois law requires that surface mines have an unmined barrier of coal 500 feet wide around active or abandoned underground mine workings. This requirement may be waived under certain conditions and surface mines have in many instances mined through all or portions of small abandoned underground mines. This may be done because the extent of the underground workings is not known or the area of the underground workings is so small that it is not worth the expense of diverting the surface operation around it. Large abandoned underground mines are commonly avoided by surface mining because the amount of recoverable coal is significantly reduced and there is a potential for large quantities of water to be present in the abandoned mine. For this study, we assumed that surface mines will obtain waivers to mine through small abandoned underground mines and to mine within 200 feet of large abandoned underground mines. Underground Minable Coal Depth of Seam The depth of coals in Illinois (most resources are less than 1,500 feet deep) is not by itself a technological restriction on mining. Coals as deep as 1,000 feet are currently being mined. However, it is more expensive to develop a mine in deeper resources, so larger mining blocks are required. Thickness of Seam For this study, 3.5 feet is the minimum thickness of available coal for underground mining. Mining thinner seams, although technologically possible, is economically unfeasible because larger reserve blocks are required, movement of miners and equipment is more difficult, normal out-of-seam dilution from the roof and floor becomes a larger percentage of the material handled, and the tonnage produced per mining cycle is reduced. These factors make it difficult to extract coal at a rate sufficient to recover the capital investment in facilities for a modern underground mine. Thickness of Bedrock and Unconsolidated Overburden Underground mining requires adequate bedrock overburden to support the mine roof and seal the mine against water seepage down from the surface (fig. 2). If the bedrock cover is too thin (or significantly weathered), the mine roof may not be strong enough to support the overburden. Unconsolidated overburden material (glacial drift and alluvium) is not self-supporting and can add considerable pressure to the mine roof and pillars. Weak underclay, which can block mine entries and make the roof unstable by squeezing out from under pillars, is commonly associated with areas where less than half of the overburden is bedrock. In addition to the dangers and expense of roof failures and floor squeezes, fractures resulting from mine roof failure may extend to the bedrock surface and allow water to enter the mine. At best, water seepage makes the movement of equipment more difficult and creates additional expenses for pumping and disposing of the water. In the worst case, the influx of water is rapid and equipment may be Table 3 Minimum thickness of bedrock and maximum thickness of unconsolidated deposits surface-minable for specified thicknesses of overburden (feet). Mininum Maximum Overburden bedrock Unconsolidated >

15 damaged and the lives of miners threatened. In 1883, 69 miners drowned in the Diamond Mine near Braidwood (Dept. of Mines and Minerals 1954). Other, less serious, cases of mine flooding have occurred over the years. A conservative rule used by some companies that is likely to guarantee good mining conditions is that the thickness of bedrock overburden should exceed the thickness of unconsolidated overburden. However, the amount of bedrock required can vary, depending on local geologic conditions such as the depth of the seam, composition of the bedrock overburden, and thickness of the glacial overburden. Rock strength tests are needed to determine the minimum bedrock for specific areas. For these studies we have used minimum thicknesses based on mining practice in nearby areas or areas with similar roof strata. We used 75 feet as the minimum thickness of bedrock for underground mining in the Tallula Quadrangle and for the Springfield Coal in the Peoria West Quadrangle. The overburden above these coals is mostly shale. Some limestone and sandstone are present above the Herrin Coal in the Peoria West Quadrangle. Because these rock types are stronger than shale, for example, greater proportions of limestone and sandstone in the bedrock mean less bedrock is needed than might otherwise be the case. We used 40 feet for the minimum bedrock cover for the Herrin Coal in the Peoria West Quadrangle. Thickness of Interburden Between Seams The interburden between two coal seams must contain competent strata of sufficient thickness so that mining of one seam will not disrupt the stability of the roof or floor of the other seam (Chekan et al. 1986). The minimum thickness of interburden required between two seams depends on several geo-technical variables, including the lithology of the interburden, the thickness and depth of the coals, and the method and sequence of mining the two seams (Hsiung and Peng 1987a, 1987b). Among the quadrangles studied for this report, only the thickness of interburden between the Danville and Jamestown Coal in the Snyder-West Union Quadrangle was of concern. The interburden consists of varying amounts of shale, siltstone, sandstone, and claystone. Where this interburden is less than 40 feet thick, only one of the coals can be mined. In this case, we assumed that the Danville Coal would be the preferred seam because of its higher quality. Faults Faults disrupt mining operations and increase mining costs by displacing the coal seam, weakening the mine roof, and creating paths for the flow of gas or water into the mine (Nelson 1981). Displacements of even a few feet are difficult or impossible for longwall equipment to negotiate. Larger displacements block all mine advancement and may require extensive tunneling through rock to reenter the coal bed on the opposite side. The amount of coal restricted from mining by faults depends on the characteristics of the specific fault. If a fault is a single sharp plane, mining can advance to it from either side and little if any coal is lost. In other cases, the zone of disturbance can be hundreds of feet wide. For example, mine operators in the Wabash Valley Fault System have encountered numerous minor faults, intense jointing, and substantial dips in the coal seam within a zone several hundred feet wide parallel to the main fault (Marvin Thompson and Alan Kern, personal communication). Some large in-flows of water and some squeezing of the floor after mining were experienced in this area. Using careful advance planning and extra exploratory drilling, operators have mined across these zones (Koehl and Meier 1983). Mining within the fault zone is kept to a minimum because of the expense and delay of supporting the weakened mine roof and altering the mine plan to work through or around displaced blocks of coal. In practice, mining operations routinely advanced to within 200 to 2,000 feet of the main fault trace (fig. 3). Because the distance of advance is dependent on conditions encountered at the time of mining, this report assumes that, on average, a zone of 1,000 feet on either side of the main fault trace will be left unmined. Partings Peat accumulation was periodically interrupted by deposition of clastic sediments from nearby streams. These layers of sediment, commonly called partings, can be a fraction of an inch to tens of feet thick. Partings can cause roof stability problems, reduce the productivity of a mine, increase the wear of mining and coal preparation equipment, reduce the efficiency of the mine s preparation plant, and increase the amount of waste material that must be stored in waste piles and slurry ponds. Partings more than a few inches thick in coal left in the mine as pillars tend to slough off and 9

16 Fault Zone Fault Zone Figure 3 Unmined areas adjacent to one of the faults in the Wabash Valley Fault System. reduce the stability of pillars (Jeffrey Padgett, personal communication). Over time, this may result in roof falls in the mine and subsidence damage to surface property. Partings may vary in number, thickness, and position within the seam (fig. 4). Partings restrict mining if they create inaccessible coal or unstable roof conditions or if the yield of clean coal (tonnage of saleable coal / tonnage of material mined) falls below an economical level. Small areas of low yield will be mined if necessary to access other reserves. Large areas with excessive parting material are not mined. Where partings are less than a few feet thick the entire seam is mined and the rock material must be separated from the coal at the cleaning plant. Because of the extra wear on equipment and the longer cutting time required, one foot of parting material is considered the maximum that is feasible to mine for any extended area. A yield of clean coal equal to 65% of the tonnage of material mined is considered by most companies to be the minimum necessary for an operation to be economic. In calculating yield for these quadrangles, we assumed 0.5 feet of out-of-seam dilution from roof and floor material, 5% loss of coal in cleaning, and specific gravities of 1.3 and 2.6 for coal and rock. If the amount of parting material exceeds the tonnage of clean coal that can be recovered, only the coal above or below a parting will be mined (if possible). For example, in figure 4a, the lower 2-plus feet of the seam consisting of coal and shale would be left in the floor, and only the upper 6-plus feet of coal would be mined. However, thick partings in the Springfield Coal adjacent to the Galatia Channel, such as shown in figs. 4d-g, have been found to present special problems. These partings thicken over such a short distance that the upper bench of coal has too steep a pitch to mine. The parting material 10

17 consists of laminated shale that is so weak it is difficult to bolt, and massive roof falls are common. The companies familiar with these conditions said they would avoid mining either bench of coal. Dykersburg Shale The Dykersburg Shale Member is a unit of light to dark gray shales, siltstones, and sandstones 10 deposited directly on the Springfield Coal in the vicinity of the Galatia Channel (fig. 5). The unit is as much as 100 feet thick adjacent to the channel and thins and pinches out from the channel for several 5 hundred feet to several miles. The Dykersburg makes a stable roof with two known exceptions: certain facies found near the Galatia Channel (described below in section on Galatia Channel ) a b c d e f g and in areas where there is an abrupt Figure 4 Examples of partings in the Springfield Coal in the change in thickness of the Dykersburg Springerton Quadrangle. over a short distance (fig. 6). In some areas the Dykersburg varies only 10 to 20 feet in thickness over a mile or more. In other areas the change in thickness is more abrupt, thinning 60 to 80 feet over less than 0.5 miles. These areas of abrupt thinning have been correlated with severe roof conditions in mines. It is not known whether the weakness of the roof in these areas is due to the effects of differential compaction of sediments, a change in facies, ancient slumps of the unlithified sediments, or a combination of these and other factors. Because of the severity of the roof falls experienced in these areas, companies avoid mining under areas of abrupt changes in the thickness of the Dykersburg. These areas are considered in this study to be unavailable for mining. feet A possible third zone of weak roof conditions may exist at the edges of the Dykersburg Shale. Mining companies reported encountering poor roof conditions in some areas of the Energy Shale (a unit above the Herrin Coal, but depositionally analogous to the Dykersburg) at the deposit s margins where the shale is about 10 to 20 feet thick (Treworgy et al. 1996b). The shale in these areas does not bond well to the overlying strata and is difficult to hold with roof bolts. Only in limited areas has coal been mined under the margins of the Dykersburg Shale. The experts we interviewed were not familiar with roof conditions in these areas. Anvil Rock Sandstone The Anvil Rock Sandstone was deposited some time after the drowning and initial burial of the Herrin peat swamp. The sandstone most commonly occurs as a sheet facies and it is present over a broad area of the southern Illinois coal field east of the Du Quoin Monocline. The sandstone is also found filling long sinuous channels that extend for miles across the western and southern portions of the coal field (fig. 7). These channels eroded down through the Herrin Coal and vary in width (at the horizon of the Herrin) from a few hundred feet to more than two miles. Adjacent to the major channels that cut through the coal are minor channels that cut down nearly to or into the top of the coal. Severe roof problems are encountered in places where the sandstone is within 5 feet of the top of the coal bed (fig. 8). In these areas, the Brereton Limestone, the preferred anchoring zone for roof bolting, is commonly missing. The interval between the coal and the sandstone is weak, particularly if the normal rock sequence has been replaced by channel scour. In addition, holes drilled into the sandstone for roof bolting allow water to enter the mine, especially if, as it is in some areas, the water is under pressure. The zone where these conditions are found extends 1,200 to 2,000 feet from the main area where the coal has been washed out. We did not have sufficient data in our study area to delineate this zone (nor will there be enough data in most areas that have only had reconnaissance drilling). We used a buffer of 1,800 feet from the main channel to represent the approximate zone where mining of the Herrin Coal is unlikely to occur due to these conditions. In practice, mining may advance closer or not so close depending on the local conditions encountered. 11

18 Mt. Carmel Albion South Springerton Galatia Figure 5 Extent of the Dykersburg Shale and the Galatia Channel and the location of quadrangles studied (from Treworgy and Bargh, 1993). Galatia Channel The Galatia Channel, a drainageway through, and contemporaneous with, the peat swamp of the Springfield Coal, has strongly influenced the thickness, quality, and minability of the Springfield Coal (fig. 5). The coal is generally thick (6 feet to more than 8 feet) in a zone along and extending from one to several miles away from this channel (Hopkins 1968). Immediately adjacent to the channel, the coal is commonly split into two or more benches separated by shale, siltstone, and sandstone a few inches to tens of feet thick. Within the course of the channel the coal is missing, and is replaced by sandstone, siltstone, and shale. Unstable roof conditions, abrupt variations in seam thickness, local washouts of the seam, and other poor mining conditions are encountered in the Springfield Coal near the Galatia Channel (fig. 6). These conditions are difficult to predict and delineate, even with data from closely spaced drill holes. Mines are commonly laid out so that areas of potential problems can be probed and abandoned if conditions are found to be unfavorable. In some areas, severe problems have been encountered as much as a mile from the channel. To estimate the amount of coal that may be unminable because of conditions related to the Galatia Channel, this study considered coal less than a half mile from the channel to be unavailable for mining. In some areas this coal 12